Why Am I Holding Water? The Science Behind Water Retention & Weight Fluctuations

Joelle Cavagnaro
March 13, 2025
5 min read

Water retention and weight fluctuations go hand in hand—most people understand that. But why? Why are you feeling “puffier” than usual? Why is your scale weight up a few pounds from day to day even when you’re executing your training and nutrition protocols properly?

What Are Some Reasons This Happens?

Some common causes of weight fluctuations or increased water retention:

  • Stress
  • Menstrual cycle changes
  • Hydration status
  • Carbohydrate intake
  • Inflammation

Some common culprits of the mechanisms behind that water retention:

  • ADH (Anti-Diuretic Hormone)
  • Aldosterone
  • Insulin

Let’s take ADH for instance. ADH stands for anti-diuretic hormone. Generally speaking, we know diuretics increase fluid output (typically urine). So, as you can imagine, anti-diuretic hormone’s purpose is to retain and conserve bodily fluids.

Example:

  • Increased stress = increased cortisol
  • Increased cortisol can bind to aldosterone receptors
  • This, in turn, increases sodium retention
  • Increased sodium retention = increased water retention

Another example of ADH at play is regarding the menstrual cycle. Progesterone is typically known as a diuretic. But there are also instances in which estrogen may be high relative to progesterone, and in such cases, ADH can be increased—leading to water retention. And well… as you may have noticed, water retention is a common PMS symptom.

That said, it’s important to note that ADH isn’t the only mechanism by which water is retained.

Let's Keep Going…

Many of us have heard the term “inflammation” thrown around in a variety of ways, especially in the health and fitness realm. NOTE: Chronic inflammation and acute inflammation are entirely different. Chronic inflammation is what we wish to avoid. Acute inflammation, on the other hand (think new injury like a broken toe), is the body’s natural response to initiating the healing/recovery process.

Example:

What happens as soon as you hurt yourself? Swelling. This swelling is the result of increased fluid and white blood cells being sent to the injured area. Have an injury that needs healing or a surgery you’re recovering from? Expect a bit of “water weight.”

Hydration & Water Retention

Another example of water retention is based on hydration status.

It sounds counterintuitive—but the less water we consume, the more water we “hold.” This is simply a conservation mechanism by the body to protect against dehydration. In efforts to conserve water, the body will increase ADH and aldosterone. Remember:

  • Increased ADH = increased fluid retention.

Additionally, we must remember that water follows sodium in the body. Therefore, if we were to have a sudden increase in sodium (compared to what our body is used to), we will hold additional water extracellularly (outside of our cells). This often causes muscles to look fuller or makes you feel “puffier.”

That said, our kidneys will take care of this by excreting the excess sodium—at which point, the extracellular water you’re “holding” would be excreted as well.

Carbohydrate Intake & Water Retention

Another example? Carbohydrate intake. You may (or may not) have heard that similar to sodium, water gets stored along with carbohydrates.

  • For each gram of carbohydrate (glycogen) stored in the body, we also store 2-3g of water along with it.
  • This is why when people switch to a low-carb diet, they appear to lose weight quickly (according to the scale). By consuming fewer carbs, they are simply depleting their glycogen stores—resulting in a loss of fluid as well.

Keep Your Cool & Ask Yourself

ALL of this to say—water weight is just that. Extra water that the body is holding or conserving temporarily for a variety of reasons. It’s not permanent and it’s not indicative of body fat gain. These are some of the MANY reasons that it’s important to be objective regarding the scale.

If your scale weight is up… ask yourself:

  • Am I more stressed than usual?
  • Am I hydrated enough?
  • Did I eat more sodium than I’m used to?
  • Am I nearing my period?
  • Did I hit a hard/heavy workout recently that my body needs to recover from?
  • Did I consume more carbohydrates than usual?

Be objective, remain calm, and stick to your plan and protocols like you would any other day.

Need help optimizing your protocols to reach your health and fitness goals? Let us help by putting an expert in your corner to help you get there faster and maintain that progress for life! Learn more about our online health coaching by clicking here!

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